Trucks such as pickup trucks and the like are often used to transport small cargo loads and/or to make deliveries and pickups. One of the difficulties of using such trucks is that of loading and unloading heavy or awkward cargo when a loading dock of proper height is not available. For example, the cargo box of a pickup truck can be three or more feet off of the ground, making it difficult to load or unload cargo to and from the cargo box.
Various attempts have been made in the past to make it easier to load and unload cargo. For example, Canadian patent application no. 2,145,259, published Sept. 23, 1995, illustrates a vehicle having a U-shaped chassis with a drop tray decking. The tray is powered by hydraulics at each corner of the decking to raise and lower the tray. However, such a system requires a sophisticated control system for activating the hydraulics to ensure that each of the hydraulic cylinders operate simultaneously.
U.S. Pat. Nos. 4,902,188 to Page and 5,288,197 to Harris show systems wherein the cargo platform of a vehicle and a trailer, respectively, is lowered by pivoting the platform rearward and downward to facilitate easier loading and unloading of cargo. These systems suffer from the fact that they require a clear space behind the vehicle or trailer to allow the cargo platform to move rearward as it is pivoted downward.
Vehicles according to U.S. Pat. No. 4,902,188 to Page were briefly offered for sale in the United States under the trademark KELPIE KARGO. However, such vehicles were not commercially successful.
Other prior art systems include U.S. Pat. No. 4,813,842 to Morton, which shows a lift gate placed on the rear of a pickup truck, but such lift gates are generally expensive and are quite heavy, thereby reducing the weight of cargo which may be carried by the truck. Further, such gates typically do not have a great depth, thereby limiting the size of the cargo which may be safely lifted or lowered with the gate.
Other prior art systems to assist in the loading and unloading of cargo have provided a ramp at the back of the cargo box so that dollies or lift carts loaded with cargo may run up or down the ramp as appropriate. Examples of such systems are shown in U.S. Pat. Nos. 4,990,049 to Hargrove and 5,342,105 to Miles. However, problems exist with these systems in that the ramp must be stored somewhere on the truck between uses and movement of cargo into and out of the cargo box relies upon the brute strength of the cargo handlers pushing the dollies and/or lift carts up and down the ramp.
U.S. Pat. No. 4,154,352 to Fowler shows a system wherein the wheels of a trailer are retracted to lower the bed of the trailer, allowing cargo to be more easily loaded or removed. However, these systems only work for trailers, and not vehicles, and suffer from poor suspension and load carrying capacity.
Other prior art systems for loading and unloading vehicles include crane-type mechanisms, as shown in U.S. Pat. No. 4,383,791 to King, hoists as shown in U.S. Pat. No. 5,201,628 to Driver and dump-type boxes, as shown in U.S. Pat. No. 5,267,779 to Talamantez et al.